For your questions:
1->Yes, there is no restrictions. Make sure a dimension is joined to any other object. It can be self join using Alias.
2->Creat a logical fact able in BMM and add DayFact and TimeFact as logical sources and set proper content levels if needed.

Since you are going with 2 different granularity, for time you might need a new dimension table as good as W_DAY_D interms minutes.
I think you might need it for analysis based on time and this also helps you to roll up to the day level.
Generally 20130214 is surrogate key for w_day_d for today's record, similarly for Time level you have to go for each minute like
1-->00:01 AM
2
3
....
60-->01:00AM
101-->01:01AM
.... like that to cover 23:59 PM